The dilation and effacement of the cervix uteri takes place both before and during labor. Second only to uterine contractions, it is necessary for the genesis of productive labor. Premature labor or nonproductive labor often coincides with excessive dilatation or the lack of proper dilatation. The resulting infant is often subnormal because of prematurity or anoxic birth. Cervical elasticity during labor would appear to be crucial to the control of labor. We plan to study the stress-strain behavior of the rabbit cervix in the presence of the prostaglandins, PGE2, PGF2 alpha, and PGE1 in order to quantify and evaluate any possible contribution of these drugs to dilatation. Non-pregnant, pregnant and labor-induced animals will be studied, as well as animals treated with prostaglandin antagonists. Strips of the cervix from these animals will be removed and stretched while the developing tension is recorded. Thus, a series of derived measurements may be obtained, one of which will be the stretch modulus, or measure of the elasticity of the tissue. With a single parameter of this sort, the various categories of animals will be statistically compared for variations, under treatment, of cervical elasticity. The importance of these studies will be to investigate the possibility of using these materials to enhance cervical softening in the human.